Year	Number
1971	12.35504
1972	12.25761
1973	11.86957
1974	12.26973
1975	11.79553
1976	12.04358
1977	12.34223
1978	12.09457
1979	11.95963
1980	11.82051
1982	12.57889
1983	12.61455
1984	12.77077
1985	13.00501
1986	13.14651
1987	13.12261
1988	13.03415
1989	13.40768
1990	13.33034
1991	12.93109
1992	12.30383
1993	11.4402
1994	11.31522
1995	11.78502
1996	10.41089
2001	10.80581
2002	10.80932
2003	10.75753
2004	10.30692
2005	10.44984
2006	10.54638
2007	11.55325
2008	11.32133
2009	11.15314
2010	10.97634
2011	11.32691
2012	11.19134
2013	11.54847